Write down the song's lyrics and the name of each chord in the melody. Proofread and play the song to make sure you have written the chords down correctly. If possible, create a demo at a recording studio or on your computer with music recording software.
Visit copyright.gov and apply for a U.S. copyright on your song to protect it from being claimed by someone else. The fee is $35 as of June 2011, and the processing time is approximately 3 months. Once the copyright is established, you will receive a certificate and copyright number.
Find a music publisher by perusing listings in online trade publications such as Billboard, ASCAP and BMI. Choose publishers interested in your genre of music. For example, don't waste time submitting a country song to a rock-only publisher. Follow their submission guidelines exactly.
Publish your music yourself by creating an audio and selling it through a self-publishing music and distribution company such as Create Space or MySpace.